Deuterium-methane exchange

Other investigations of methane activation by Sehested [415] showed a strong impact of alkali on the methane/deuterium exchange reaction as illustrated in Table 6.2. 

Protonated methanes and their homologues and derivatives are experimentally indicated in superacidic chemistry by hydrogen-deuterium exchange experiments, as well as by core electron (ESCA) spectroscopy of their frozen matrixes. Some of their derivatives could even be isolated as crystalline compounds. In recent years, Schmidbaur has pre-... 

Studies of the photochemical formation of benzyl carbanions have been reported for two systems this year. Ultra-violet light irradiation of (420) in aqueous acetonitrile resulted in formation of (421) exchange of the benzylic hydrogens of (420) was also observed when heavy water was used in the solvent. Compound (421) was shown to arise by two pathways a di-7r-methane rearrangement, and a 1,7-hydrogen shift followed by electrocyclic closure. The deuterium exchange reaction is presumed to occur due to... 

The equilibrium constant for the third, deuterium exchange, reaction is around 2 at the temperature at which the second, water-gas shift, reaction is carried out. Because an excess of water is used to convert CO completely to COj, the deuterium content of hydrogen will be less than that of the methane and water fed, unless the excess water is fully recycled. Because water recycle is usually not practiced at ammonia synthesis plants, the deuterium content of synthesis gas at operating plants is sometimes as low as 0.009 percent [M7]. If the ammonia plant were specifically designed for deuterium recovery from its synthesis gas, the deuterium content could be increased to the average of the methane and water feeds by recycling aU water and preventing losses. 

Superacid DF-SbFs induces protium-deuterium exchange in isobutane [54b]. Strong acids (BF3, BFj-HjO, HF-BFj, CF3SO3H)catalyze carbonylation of alkanes including methane by carbon monoxide [54c], whereas sulfuric acid can induce carbonylation of iso- and cycloalkanes [54e,d]. In both cases, carboxylic acids are obtained. The elimination of molecular hydrogen from alkyl can occur (see a recent theoretical study of the Hz elimination from CzHs [54f]). 

B. Schools, J. A. Martens, P. A. Jacobs, R. A. Schoonheydt, Kinetics of hydrogen-deuterium exchange reactions of methane and deuterated acid FAU- and MFI-type zeolites, J. Catal., 1999, 183, 355-367. 

The initial vague ideas about the mechanism were formulated by industrial groups around 1970 [22] [381], whereas only few academic scientists were involved in studies of the reaction. This included the groups around Temkin [58], Balandin [35], Borowiecki [36], Trimm [304] and Ross [373]. The activation of methane was studied in the 1960s by Kemball [270] by deuterium exchange studies also applied by Frennet [198]. 

As an example we discuss predictions for the rate constant of the proton-deuterium exchange reaction between deuterated methane and the zeolite cluster of Figure 6.17... 

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